Industrial processes may use centrifugal fans to supply relatively clean, dry air to industrial systems. Among the many applications that may require supply air include thermal oxidation, glass tempering, and waste water treatment. The size of the fan and the accompanying fan impeller may depend on the application in which the fan is used.
A conventional fan impeller may include a circular front plate, a circular back plate, and blades between the front and back plate. The front plate of the fan impeller may include a concentric, circular air inlet through which air enters the fan. The front plate may also form a curved lip around the periphery of the air inlet and around the periphery of the front plate itself. The curved lips may be formed by stamping the front plate in a die or spinning the front plate on dedicated tooling. The curved lips at the circumference of the air inlet and the front plate provide benefit with regard to air performance and strength by increasing stiffness. The back plate may be a similarly-sized, circular plate concentric with the front plate. Blades may be positioned between and attached to the front plate and the back plate. The blades of a conventional fan impeller may include an outer edge, conventionally known as a trailing edge, and an inner edge, conventionally known as a leading edge. Additionally, conventional fan impellers may be made of metal, such as steel, with the blades welded to the front plate and the back plate. A conventional fan impeller may also include a hub attached to the back plate to serve as the means of attachment of the fan impeller to a fan shaft.
Fan impellers are often described by the size of their inner diameter and outer diameter. The inner diameter is the length of the line segment passing through the center of the fan and terminating at the circumference of the air inlet. The outer diameter is the length of the line segment passing through the center of the fan and terminating at the circumference of the front plate or the back plate. The blades may have a length such that they may be positioned and extend between the inner diameter and outer diameter of the front plate and the back plate. The size of the outer diameter is a function of the blade length and will increase as the blade length increases.
The air flow and static pressure output of a fan may depend on the speed of the fan impeller, the blade width, or the blade length. It is often desirable to modify the air flow or static pressure output of a fan, for example, due to increased system demands. In situations where industrial fan systems are locked into a specific fan speed, modification of the fan impeller geometry may be one of very few, or possibly the only alternative to increase the air flow or the static pressure output. Conventional methods of modifying fan impellers include increasing the blade width or the blade length to modify the air flow or the static pressure output. Increases in blade length may require modifications to the diameters of the front and back plate in order to accommodate the longer blades.
However, increasing the outer diameter of the front plate may be a labor and cost-intensive process due to the curved lips formed around the circumference of the air inlet and the front plate. Conventional fabrication techniques may continuously weld a curved lip at the outer diameter of a flat, circular plate, which may then be used as a front plate. Alternatively, the stamping tooling may be disassembled and modified to create two separate inner and outer pieces with properly formed lips at the inner diameter and outer diameter. These pieces must then be continuously welded to join them as a single front plate. Thus, conventional fabrication methods may require special parts that demand tooling reconfigurations and modifications adding additional time and labor.
Methods to mitigate these difficulties have been attempted. One method that has been attempted modifies the outer edge of the blades, which only requires a modified back plate. A tapered outer edge is added to the blade such that the outer edge forms a slope between the front plate and the back plate.
The tapered outer edge results in a blade having one side edge longer than the corresponding opposite side edge. The shorter side edge of the blade is attached to the front plate, and the longer side edge is attached to the back plate, which eliminates the need to modify the front plate. Thus, only the back plate requires modification to accommodate the longer side edge of the blade. Because the back plate is fabricated via traditional metal cutting operations and not dedicated tooling, increase in labor for the manufacture of the back plate may be controlled.
However, while this method addresses the difficulty of modifying the front plate, the increase in the air flow or the static pressure output of the fan may be insufficient. Thus, it would be desirable to provide a fan impeller blade whose overall length may be increased without resource-intensive fabrication methods that provide for further improvements to and fine tuning of the air flow or the static pressure output of the fan.